Vibration isolation system particularly adapted for use with a chain saw

ABSTRACT

An improved vibration isolation system particularly adapted for use with a chain saw and characterized by a diaphragm, journaled on shaft means, and engaged on either side by resilient impedance means. The shaft means may be connected with a vibrating assembly which includes a chain saw engine and cutter chain, while the diaphragm means may be connected with a support means within which the vibrating assembly is resiliently supported.

States atent [1 1 Frederickson et a1.

[75] Inventors: Robert Eugene Frederickson, South Gate; Walter Joseph Hammond, Lakewood, both of Calif.

[73] Assignee: McCullough Corporation, Los

Angeles, Calif.

[22] Filed: May 15, 1973 [21] Appl. N0.: 360,561

[52] 11.5. C1 30/381, 173/162, 248/22, 248/358 R [51] Int. Cl B27b 17/02, F16f 7/12 [58] Field of Search 30/1234, 381-389; 173/162; 248/15, 18, 22, 24, 358 R; 267/141, 137

[56] References Cited UNITED STATES PATENTS 2,352,049 6/1944 Weaver.., 248/358 R June 4,1974

2,415,280 2/1947 Fink 248/358 R 2,441,766 5/1948 Jardine 173/162 3,430,902 3/1969 Lohr 248/358 R 3,542,095 11/1970 Frederickson 30/381 [57] ABSTRACT An improved vibration isolation system particularly adapted for use with a chain saw and characterized by a diaphragm, journaled on shaft means, and engaged on either side by resilient impedance means. The shaft means may be connected with a vibrating assembly which includes a chain saw engine and cutter chain, while the diaphragm means may be connected with a support means within which the vibrating assembly is resiliently supported.

7 Claims, 5 Drawing Figures VIBRATION ISOLATION SYSTEM PARTICULARLY ADAPTED FOR USE WITH A CHAIN SAW BACKGROUND, OBJECTS, AND SUMMARY OF INVENTION This invention constitutes an improvement in relation to a vibration isolation system, particularly adapted for use with internal combustion engine operated chain saws, and described in U.S. Frederickson Pat. No. 3,542,095, US. Frederickson et al. Pat. No. 3,652,074, and US. Frederickson et al. Pat. No. 3,698,455.

Each of these Frederickson et al. patents pertains to an improved vibration isolating chain saw where a support means, including handle means and inertia means, define a cradle-like structure within which a vibrating assembly is resiliently supported. The vibrating assembly includes a chain saw driving, internal combustion engine and a guide bar and cutter chain assembly.

In the preferred embodiments described in the aforesaid Frederickson 'et al patents, vibration isolating means are interposed between the top of the engine assembly and underside of the inertia means. Another vibration isolating means is interposed between the bottom of the engine assembly and the support means.

The structures featured in the aforesaid Frederickson et al patents are believed to constitute a particularly significant advance in the art of minimizing chain saw vibration. Nevertheless, and particularly with respect to the lower vibration isolating mount which is interposed between the support means and the underside of the engine assembly, it is believed that significant improvements may be yet effected.

For example, it is believed that it would be desirable to optimize shock absorbing ability in a direction extending longitudinally of the guide bar andcutting chain, i.e., longitudinally of the cutting path, while maintaining a greater degree of stiffness, coupled with a shock absorbing ability, in a multiplicity of directions extending transversely of this longitudinal direction. In particular, it is believed desirable to maintain this relatively greater stiffness in a generally radial pattern, including both up and down and side to side directions.

It is likewise believed desirable to provide an improved vibration isolation unit which would yield the benefits of a diaphragm-type shock absorbing action while minimizing the tendency of the diaphragm to break or undergo damage due to prolonged usage.

It is likewise believed that it would be desirable to provide a shock absorbing unit, particularly suited for use with a chain saw, which would be resiliently operable in compression to absorb shock in both up and down and side to side directions while maintaining an ability to absorb cutter chain generated shocks, which are oriented generally longitudinally of the cutting direction, in a shear mode, and while attaining the foregoing desirable objectives.

Bearing these overall objectives in mind, it is believed that they are accomplished to a substantial extent in the context of a chain saw having a vibrating assembly which includes an engine having a crank shaft and also includes a cutter chain means which traverses a cutting path. This chain saw context of the invention additionally includes support means including handle means. A plurality of vibration isolation means, in this type of chain saw, serve to interconnect the vibrating assembly and support means.

The improvement aspect of the invention involves unique, structural characteristics of at least one of the aforesaid vibration isolation means.

Structural aspects of this improvement concept entail the use of a resilient diaphragm means having an aperture and which extends generally transversely of the cutting path. A shaft means passes through the aperture of the diaphragm means, with the diaphragm means being journaled upon the shaft means.

A first, resilient, impedance means, mounted on the shaft means, abuttingly and separably engages one side of the diaphragm means. A second, resilient, impedance means, mounted on the shaft means, abuttingly and separably engages the opposite side of the diaphragm means. A first mounting means connects the diaphragm means with one of the vibrating assembly and support means. A second mounting means serves to connect the shaftmeans with the other of the vibrating assembly and the supportmeans.

In a preferred arrangement, the resilient diaphragm means extends generally parallel with the axis of rotation of the engine crank shaft.

In the preferred embodiment, the diaphragm means includes a mounting wall portion surrounding the aperture and the first and second resilient impedance means define a generally annular recess within which this mounting wall portion is both radially slideably and rotatably received.

The wall portion may have flat parallel sides, with the generally annular recess having flat parallel annular wall portions contiguous with the flat parallel sides of the mounting wall portion. Alternatively, the mounting wall portion may have a convex, generally annular terminus surrounding the diaphragm means aperture. In this arrangement, it is contemplated that the generally annular recess would have a generally concave, outwardly facing base, facing and engaging the generally convex terminus.

Another embodiment of the invention involves an arrangement where each vibration isolating unit, interconnecting a vibrating assembly of a chain saw with a support means, would be characterized by one or more of various vibration isolation means structural characteristics heretofore delineated.

As an independent aspect of the invention, and not limited to the chain saw environment, it is contemplated that the invention involves a vibration isolating unit characterized by the various structural characteristics of a vibration isolation unit heretofore set forth, either in the sense of the individual invention aspects heretofore described or in the sense of the overall combination of these distinguishing aspects.

In describing the invention by way of example, but not by way of limitation, reference will be made to certain appended illustrations set forth in drawings which comprise a portion of this presentation.

DRAWINGS FIGS. 1 thru 5 of the appended drawings illustrate various structural aspects of preferred embodiments of the present invention.

FIG. 1 schematically depicts a vibration isolation system of the general type generally featured in US. Frederickson et al. Pat. Nos. 3,542,095, 3,652,074, and/or 3,698,455 wherein the lowermost of three disclosed vibration isolation units are fabricated and installed in accordance with the present invention;

FIG. 2 provides an enlarged sectioned side elevational view of the vibration isolation unit of the present invention which is incorporated in the FIG. 1 assembly beneath an engine assembly and above a lower handle portion;

FIG. 3 provides a transverse sectional view, in an enlarged format, as viewed along the section line 33 of FIG. 1, and illustrating the general mounting of the FIG. 2 vibration isolation unit;

FIG. 4, in a perspective and exploded" format, illustrates the separated components of the FIG. 2 vibration isolation unit; and

FIG. 5, presents a modified form of the FIG. 2 vibration isolation unit, again presented in sectioned, side elevation, and illustrating a modified cooperation between the diaphragm means of the vibration isolation unit and the resilient impedance means.

With the various drawing figures having been described, it is now appropriate to consider structure aspects of the invention as presented in these figures.

DETAILED DESCRIPTION OF INVENTION Before treating the improvement aspects of the invention, a brief summary of the preferred, chain saw context of the invention will first be discussed.

PREFERRED CHAIN SAW CONTEXT OF INVENTION The preferred arrangement for practicing the invention involves the cradle-like vibration isolation systems featured in the aforesaid Frederickson et al. US. Pat. Nos. 3,542,095, 3,652,074, and 3,698,455.

As set forth in each of these patents, a chain saw 1 includes a vibrating assembly 2 including an engine assembly 3. Engine assembly 3 includes a crank shaft having a rotational axis generally depicted by the reference numeral 4.

Chain saw 1 additionally includes a cutter chain means 5 comprising a guide bar 6 upon which a cutter chain 7 is slideably supported. By virtue of driving means now well known in the art, engine means 3 serves to drivingly cooperate with the cutter chain means 7.

As is described in the aforesaid Frederickson et al. patents, the vibrating assembly 2 is cradled within a support means 8. This support means 8 may comprise a laterally extending handle means 9, a longitudinally extended handle means 10, and an inertia or dampening means 11. This inertia or dampening means lll may comprise a fuel tank.

The manner in which the components 9, it), and 11 of the support means 8 are structurally interrelated may be appreciated by reviewing the disclosures of the aforesaid F rederickson et a] patents, the disclosures of which are herein incorporated, in their entirety by reference.

A plurality of vibration isolation means serve to inter connect the vibrating assembly 2 with the support means 8.

It is contemplated that at least three such vibration isolating means would be employed, but obviously a number in excess of three may be employed, depending upon the requirements of a particular chain saw.

Thus, as is generally described in the aforesaid Frederickson et al. patents, three vibration isolating means 12, 13 and 14 are provided in chain saw I.

The uppermost vibration isolating means l2 and 13, as shown in FIG. 1, are interposed between the top of the engine assembly 3 and beneath the inertia or fuel tank means 1!. The general arrangement of the structure and mounting for these vibration isolating means 12 and 13 may be appreciated by making reference to the foregoing Frederickson et al. patents.

The third vibration isolation unit 14, which may be interposed between the top of the lower leg 15 of the handle means it) and the underside 16 of the engine assembly 3, constitutes the improvement aspect of this invention and differs materially in a species format from the lowermost vibration isolation units featured in the aforesaid Frederickson et al. patents. The species difference notwithstanding, it will be recognized that the general arrangement depicted in FIG. 1 and described in this application corresponds to the broader, vibration isolation invention described and claimed, in particular, in US. Frederickson et al. Pat. No. 3,542,095.

Bearing these criteria in mind, it now becomes appro priate to consider detailed aspects of the improved vibration isolation unit 14.

IMPROVED VIBRATION ISOLATION UNIT Structural details of the improved vibration isolation unit of the present invention are illustrated in FIGS. 1, 2 and 3, with respect to one preferred embodiment. FIG. 4 further illustrates this preferred embodiment in a separated component format.

As shown in these figures, vibration isolation unit 14 includes a generally annular, resilient diaphragm means 17 having a central aperture 18. As will be apparent from viewing FIGS. l and 2, the plane ofthe diaphragm 17 extends transversely of the plane of the cutting path defined by the guide bar 6 and and cutter chain 7 and extends in the illustrated embodiment generally parallel with the axis 4 of rotation of the engine crank shaft. A hollow shaft 19 passes through the aperture 18 of the diaphragm 17. However, the diaphragm I7 is journaled upon the shaft 19 so as to be relatively rotatable with respect to the shaft 19.

A first, resilient, generally annular impedance means 20 is fixedly mounted on one end of the shaft means 19. This impedance means 20 serves to abuttingly and separably engage one side 21 of the diaphragm means 17. A second, generally annular and resilient impedance means 22 is mounted on the other end of the shaft means 19 and abuttingly and separably engages an opposite side 23 of the diaphragm means 17.

The diaphragm means 17, and first and second impedance means 20 and 22, may be fabricated of synthetic or natural rubber or other elastic material such as neoprene. The composition of the material of the diaphragm may vary, depending upon the emperically determined vibration isolation requirements of a particular chain saw, as well as the conditions in which the saw must operate.

It is contemplated that the first and second impedance means 20 and 22 would be bonded to steel shaft means 19 by conventional, elastomer-metal bonding techniques. Similarly a generally cylindrical steel mounting ring 24 may encircle and be bonded to the outer periphery of diaphragm means 17. In the preferred embodiment, the outer periphery of the diaphragm means 17 enlarges in each of oppositely directed longitudinal directions, thereby affording optimum strength at the juncture between the diaphragm means 17 and the mounting ring or cylinder 24.

Referring now to FIGS. 1 and 3, the mode of mounting of the vibration isolation unit 14 may now be appreciated.

A first mounting means 26 may serve to rigidly connect the diaphragm means 17 with the handle portion 15 of the support means 8.

As shown in FIG. 3, this first mounting means 26 may comprise a generally C shaped mounting collar 27 having a concave, annular mounting surface 28. This surface 28 is operable to conformingly and contiguously engage the upper portion of the ring or cylinder 24. Threaded fastener means 29 and 30 may serve to clamp the mounting C" collar 27 to the handle portion 15 so as to in essence clamp the ring 24 and diaphragm l7 rigidly to the portion 15 of the support means 8.

This mounting arrangement-may be facilitated, if desired, by providing a recess or seat 31 on the upper portion of the handle means 15. This seat may socketingly receive the lower portion of the diaphragm supporting ring or cylinder means 24.

A second mounting means 32, depicted generally in FIG. 1 and 3, may serve to connect the shaft means 19 with the vibrating assembly 2.

Second mounting means 32 may comprise a generally L" shaped bracket 33, welded to the underside 16 of engine housing portion 34 of the engine assembly 3. A tang-like portion 35 of bracket means 32 extends downwardly and is apertured to receive a mounting bolt 36. Mounting bolt 36 having a head portion 37, may pass through the interior of hollow shaft means 19. A threaded fastener means, such as a nut 38, may engage an opposite end of the threaded bolt means 36 so as to clamp the shaft means 19 rigidly against the right side of the tang portion 35 shown in FIG. 1.

With this arrangement the bolt head portion 37 would abuttingly engage the right end 39 of the hollow shaft means 19 (or a washer means engaged therewith) while the left end 40 of the shaft means 19 would abuttingly engage the portion of the mounting tang 35 which encircles the aperture of the tang and through which the bolt 36 passes (or a washer means engaged therewith). Fastener 38 will serve to clamp bolt 36 and shaft 19 fixedly to tang 35.

As will be appreciated, with this arrangement, the diaphragm means 17 will fluctuate or oscillate in a direction extending longitudinally of the cutting direction of the cutter chain means 7, and will function in shear in this direction to absorb cutting chain generated shock oriented in this longitudinal direction.

With respect to side to side (i.e., lateral) or up and down movements of the chain saw, a compressive type interaction between the diaphragm means 17 and the assemblies 2 and 8 will exist. Vibrations oriented in up and down or side to side directions will thus tend to be absorbed in a compressive mode.

Torsional interaction between the support means 8 and the vibrating assembly 2 will be readily accommodated, without stress, by the journaled relationship between the diaphragm means 17 and the shaft means 19 which accommodates relative rotation therebetween.

Extreme fluctations, in a radial sense, of the diaphragm means 17 relative to the shaft means 19 will be uniquely accommodated in view of the manner in which the diaphragm means 17 is radially slideably received between the impedance means 20 and 22.

The presence of the impedance means 20 and 22, in contiguous although separable engagement with opposite sides of the diaphragm means 17, will afford unique shock absorbing action while minimizing rupture or damage tendencies which would tend to occur at any fixed juncture between these components.

The separable nature of the impedance means 20 and 22 relative to the diaphragm means 17, and the journaled nature of the diaphragm means 17 relative to the shaft means 19, may be best appreciated by viewing the components of the vibration isolation unit 14 shown in their separated condition in FIG. 4.

As shown in FIG. 4, the shaft 19 and the impedance means 20 and 22 constitute one separable component of the unit 14, while the diaphragm 17 and mounting cylinder or ring 24 constitute another separable component. When these two components are assembled, by forcing the shaft 19 and one impedance means through the aperture 18, the assembled configuration shown in FIG. 2 is achieved.

In the assembled configuration shown in FIG. 2, the diaphragm 17 includes a mounting wall portion 41 which surrounds the aperture 18. The generally annular, resilient, impedance means 21 and 22 defined a generally annular mounting recess 42 within which the mounting wall portion 41 is radially slideably and rotatably received. 7

In the FIGS. 1 through 4 embodiment, the mounting wall portion 41 has flat parallel sides 43 and 44 surrounding the diaphragm aperture 18. The annular recess 42 has generally flat, parallel, annular wall portions 45 and 46 which are disposed in generally contiguous relation with the flat parallel sides 43 and 44 of the mounting wall portion 41.

ALTERNATIVE STRUCTURE FIG. 5 illustrates a somewhat modified form of the vibration isolation unit 14.

In this modified form a diaphragm means 17 is provided which has a convex, generally annular terminus 47. This terminus has a central aperture 18'.

Generally frusto-conical impedance means 20 and 22 cooperate to define a generally annular recess 42. This generally annular recess has a generally concave, outwardly facing base 48 which faces and engages the convex terminus 47.

It is believed that the hemispherical seat, rolling cooperation between terminus 47 and recess base 48 may contribute to efiective shear type shock absorbing action in a longitudinally directed orientation while uniquely prolonging the operating life of the components of the vibration isolation unit.

With respect to either of forms of the vibration isolation unit heretofore described, and with respect to other modifications falling within the scope of the invention, it is contemplated that in certain instances a journaled diaphragm type isolation unit of this inven tion may be used in lieu of both or either of the vibration isolation units 12 and/or 13.

As will also be recognized, a wide variety of mounting arrangements may be employed for the installation of the improved vibration isolation units of the present SUMMARY OF MAJOR ADVANTAGES AND OVERALL SCOPE OF THE INVENTION In describing the invention various advantageous aspects have been delineated.

A principal advantage of the invention is believed to reside in the basic simplicity and ease of mounting and servicing of the improved vibration isolation unit of the invention in conjunction with its ability to undergo prolonged operating life.

Another major advantage of the invention is believed to reside in the manner in which the journaled and separable nature of the diaphragm means 17 relative to the impedance means associated therewith, serves to prolong the operating life of the vibration isolation unit while minimizing the tendancy for structural damage to occur to the unit as a result of prolonged or intensive vibration absorbing operation.

Other significant advantages of the invention are believed to reside in the manner in which the improved vibration isolation unit affords a unique, anisotropic shock absorbing action. In this anisotropic shock absorbing action, cutter chain induced shock and/or engine induced vibration, oriented in a generally longitudinal direction with respect to the cutting path, is absorbed in a shear phenomenon involving axially directed oscillations of the diaphragm means. With respect to either lateral or up and down interaction between the support means and the vibrating means of the chain saw or any radially directed interaction, shock or force is absorbed in a generally radially uniform manner, with the components of the vibration isolation unit operating in compression.

Those skilled in the chain saw vibration isolating art and familiar with the disclosure of this invention may readily envision additions, deletions, substitutions or other modifications with respect to the disclosure heretofore set forth, all of which would fall within the preview of the invention as set forth in the appended claims.

What is claimed is:

1. In a chain saw having a vibrating assembly including an engine having a crankshaft and cutter chain means traversing a cutting path; support means including,

handle means; and

a plurality of vibration isolation means interconnecting said vibrating assembly and said support means;

the improvement comprising:

at least one of said vibration isolation means includmg resilient diaphragm means having an aperture and extending transversely of said cutting path; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means; first, resilient, impedance means, mounted. on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means;

first mounting means connecting said diaphragm means with one of said vibrating assembly and said support means; and

second mounting means connecting said shaft means with the other of said vibrating assembly and said support means. 2. In a chain saw having a vibrating assembly including an engine having a crankshaft and cutter chain means traversing a cutting path; support means including handle means; and a plurality of vibration isolation means interconnecting said vibrating assembly and said support means;

the improvement comprising:

at least one of said vibration isolation means includmg resilient diaphragm means having an aperture, extending transversely of said cutting path, and extending generally parallel with the axis of rotation of said crankshaft; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means; first, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means; first mounting means connecting said diaphragm means with one of said vibrating assembly and said support means; and second mounting means connecting said shaft means with the other of said vibrating assembly and said support means. 3. A chain saw as described in claim 2: wherein said diaphragm means includes a mounting wall portion surrounding said aperture; and wherein said first and second resiiient impedance means define a generally annular recess within which said mounting wall portion is radially slidably and rotatably received. 4. A chain saw as described in claim 3: wherein said mounting wall portion has fiat parallel sides surrounding said aperture of said diaphragm means; and wherein said generally annular recess has flat parallel annular wall portions continguous with said flat parallel sides of said mounting wall portion. 5. A chain saw as described in claim 3: wherein said mounting wall portion has a convex,

generally annular terminis surrounding said aperture of said diaphragm means; and wherein said generally annular recess has a generally concave, outwardly facing base, facing and engaging said generally convex terminis. 6. A chain saw as described in claim 3 where each of said plurality of vibration isolation means includes:

resilient diaphragm means having an aperture and extending transversely of said cutting path; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means;

7. A vibration isolating unit comprising:

resilient diaphragm means having an aperture;

shaft means passing through said aperture of said diaphragm means, with said diaphragm means being joumaled upon said shaft means;

first, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; and

second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means. 

1. In a chain saw having a vibrating assembly including an engine having a crankshaft and cutter chain means traversing a cutting path; support means including handle means; and a plurality of vibration isolation means interconnecting said vibrating assembly and said support means; the improvement comprising: at least one of said vibration isolation means including resilient diaphragm means having an aperture and extending transversely of said cutting path; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means; first, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means; first mounting means connecting said diaphragm means with one of said vibrating assembly and said support means; and second mounting means connecting said shaft means with the other of said vibrating assembly and said support means.
 2. In a chain saw having a vibrating assembly including an engine haVing a crankshaft and cutter chain means traversing a cutting path; support means including handle means; and a plurality of vibration isolation means interconnecting said vibrating assembly and said support means; the improvement comprising: at least one of said vibration isolation means including resilient diaphragm means having an aperture, extending transversely of said cutting path, and extending generally parallel with the axis of rotation of said crankshaft; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means; first, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means; first mounting means connecting said diaphragm means with one of said vibrating assembly and said support means; and second mounting means connecting said shaft means with the other of said vibrating assembly and said support means.
 3. A chain saw as described in claim 2: wherein said diaphragm means includes a mounting wall portion surrounding said aperture; and wherein said first and second resilient impedance means define a generally annular recess within which said mounting wall portion is radially slidably and rotatably received.
 4. A chain saw as described in claim 3: wherein said mounting wall portion has flat parallel sides surrounding said aperture of said diaphragm means; and wherein said generally annular recess has flat parallel annular wall portions continguous with said flat parallel sides of said mounting wall portion.
 5. A chain saw as described in claim 3: wherein said mounting wall portion has a convex, generally annular terminis surrounding said aperture of said diaphragm means; and wherein said generally annular recess has a generally concave, outwardly facing base, facing and engaging said generally convex terminis.
 6. A chain saw as described in claim 3 where each of said plurality of vibration isolation means includes: resilient diaphragm means having an aperture and extending transversely of said cutting path; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means; first, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means; first mounting means connecting said diaphragm means with one of said vibrating assembly and said support means; and second mounting means connecting said shaft means with the other of said vibrating assembly and said support means.
 7. A vibration isolating unit comprising: resilient diaphragm means having an aperture; shaft means passing through said aperture of said diaphragm means, with said diaphragm means being journaled upon said shaft means; first, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging one side of said diaphragm means; and second, resilient, impedance means, mounted on said shaft means, and abuttingly and separably engaging an opposite side of said diaphragm means. 